1. Technical Field
The present invention relates to a translation method and translation system based on patterns, and particularly to a translation system which is based on translation patterns.
2. Description of the Related Art
As the Internet comes into widespread use, more and more documents written in foreign languages are being accessed. As a tool to translate such documents into a native language, machine translation systems are rapidly becoming widespread. However, in an environment such as the Internet, where information in a wide variety of fields is available for access, a single word may have a quite different meaning and even be translated differently depending on the fields. Therefore, customizing a translation system according to a field is important for the users and developers of a translation system.
One such method of customization involves adding words to or changing words in a dictionary, or modifying grammatical rules used for the system. Such customization requires expertise and in addition, is likely to increase ambiguities due to the inconsistency of terms or grammatical rules. Therefore, improvement of translation accuracy or proper selection of terms according to fields is not always possible.
Thus, in recent years a machine translation system using translation patterns has come to attention and has been commercialized. In this system, a large number of translation patterns for each word, clause, phrase, or sentence in a source language corresponding to those in a target language are provided in advance. A part of a text (a sentence or word) written in the source language is matched against the translation patterns to take the text as a mosaic comprising a number of translation patterns. Then, the source language is translated into the target language based on those translation patterns. Although such a method requires a large number of translation patterns, it has the significant advantage that such a system can easily be customized because the user can define translation patterns easily.
Published Unexamined Patent Application No. 5-290082 discloses a translation apparatus which matches text written in a source language against a plurality of translation patterns provided in advance, then translates the text based on the results. FIG. 11 shows an example of translation patterns used in the prior art. As can be seen, a number of translation patterns are provided, each of which is comprised of a source language pattern, a variable representing that source language pattern with one character, and a target language pattern corresponding to that source language pattern. Some translation patterns are represented by a nested structure which contains a variable representing another translation pattern. However, with this prior art, the range of language patterns which can be matched by one translation pattern is very narrow, because only one variable is provided for each translation pattern. This would be a particularly serious problem in a case where the part of speech of the source language pattern differs from that of the target language pattern.
Source language pattern: "worry about" PA1 Target language pattern: "shimpai da"
In the above example, the pattern of speech of the source language pattern is a verb, whereas the pattern of speech of the target language pattern is an adjective. In such a case, the target pattern cannot be represented by a single variable in prior art.
In addition, in the prior art a variable representing a source language pattern cannot have information which is held by that pattern. For example, although a noun in singular form and a noun in plural form in English are similar in representation, they cannot be distinguished by a single translation pattern, and different patterns must be used for the respective forms.
Due to the above-mentioned reasons, the number of representations which can be matched by one translation pattern are limited, so that a large number of translation patterns must be provided in order to generate accurate translations.